<!DOCTYPE html>
<html lang="en">
	<head>
		<title>GET VIDEO</title>
		<meta charset="utf-8">
	</head>
	<body>
	<input type="button" title="开启摄像头" value="开启摄像头" onclick="getMedia()" />
	<video id="video" width="500px" height="500px"  ></video>
	<canvas id="canvas" width="500px" height="500px"></canvas>
	<button id="snap" onclick="takePhoto()">拍照</button>
	<script>


    alert(navigator.mediaDevices)

    let constraints = {
      audio: true,
      video: {
        width: { min: 1024, ideal: 1280, max: 1920 },
        height: { min: 776, ideal: 720, max: 1080 }
      }
    }

    navigator.mediaDevices.getUserMedia(constraints)
.then(function(mediaStream) {  })
.catch(function(error) { alert(JSON.stringify(error)) })
        function getMedia() {
            let constraints = {
                video: {width: 500, height: 500},
                audio: true
            };
            //获得video摄像头区域
            let video = document.getElementById("video");
            //这里介绍新的方法，返回一个 Promise对象
            // 这个Promise对象返回成功后的回调函数带一个 MediaStream 对象作为其参数
            // then()是Promise对象里的方法
            // then()方法是异步执行，当then()前的方法执行完后再执行then()内部的程序
            // 避免数据没有获取到
            let promise = navigator.mediaDevices.getUserMedia(constraints);
            promise.then(function (MediaStream) {
                video.srcObject = MediaStream;
                video.play();
            });
        }
 
      function takePhoto() {
      //获得Canvas对象
      let video = document.getElementById("video");
      let canvas = document.getElementById("canvas");
      let ctx = canvas.getContext('2d');
      ctx.drawImage(video, 0, 0, 500, 500);
      }
</script>
</body>
</html> 